The present invention relates in general to communication systems and components, and is particularly directed to a new and improved printed circuit board-configured dipole antenna array architecture, containing a plurality of parasitic elements that are spatially arranged in planes offset from and parallel to the plane containing the array of dipoles of the antenna, so as to provide a reduction in the sidelobes of the antenna array""s radiation pattern.
Communication system designers are constantly seeking ways to improve the performance of system components and signal processing circuits, without incurring a substantial cost or hardware complexity penalty. For example, radio wave system designers desire to maximize the collection or emission of desired electromagnetic energy and to minimize the coupling of unwanted radiation with respect to the system""s antenna. In communication systems that employ dipole antennas and arrays, such as those mounted on aircraft, for example, improvements in directivity gain can be obtained by Yagi antenna configurations that employ parasitic elements in proximity to driven dipole radiators. For an illustration of documentation that describes use of parasitic elements in antenna architectures, especially for improving directivity gain, including those employing dipole antennas, attention may be directed to the Finneburgh U.S. Pat. No. 2,897,497; Cermignami et al, U.S. Pat. Nos. 4,186,400 and 4,514,734; Coe et al, U.S. Pat. No. 4,812,855; and Podell, U.S. Pat. No. 5,612,706.
In high user density environments such as cellular wireless systems, mutual interference is perhaps the most significant problem. Although cell and channel assignment algorithms provide some measure of interference rejection, the fact remains that optimal performance requires that systems of this type have the ability to maximize energy coupling (such as between a subscriber unit and a base station) in a relatively narrow main lobe (namely, place the antenna""s main lobe xe2x80x98right on topxe2x80x99 of a target emitter/receiver). In addition, they should reduce/minimize, to the extent possible, energy that is present in lobes other than the main beam, namely from sources (of interference) other than that lying in the main beam.
In accordance with the present invention, this objective is achieved in a dipole antenna array, such as a phased array dipole antenna for producing a relatively narrow steerable beam, by providing a plurality of parasitic antenna elements that are arranged in planes parallel to and spaced apart from the dipole elements of the array, so as to effectively reduce unwanted sidelobes in the radiation pattern produced by the array.
Pursuant to a preferred embodiment of the invention, the driven elements of the dipole array and one or more director elements are formed as patterned conductor elements on a first, generally planar driven array-supporting dielectric substrate. Feed elements for the driven dipole array also include conductor elements formed on a second, opposite surface of the first, driven dipole array-supporting substrate. The feed elements have a geometry and mutually overlapping projection relationship with the conductors of the driven dipole elements, so as to form a matched impedance transmission line through the dielectric substrate with the driven dipole elements.
In addition, one or more parasitic (electrically floating) conductor elements are formed on a second, auxiliary dielectric substrate that is arranged parallel to and is spaced apart from a first side of the first dielectric substrate. These additional parasitic conductor elements are oriented parallel to the driven elements and function to reduce sidelobes in the radiation pattern exhibited by the antenna array. In like manner, one or more further parasitic conductor elements are formed on a third, auxiliary dielectric substrate that is arranged parallel to and is spaced apart from a second side of the first dielectric substrate. These further parasitic conductor elements are also oriented parallel to the driven elements on the first dielectric substrate and function to reduce sidelobes in the radiation pattern exhibited by the antenna array.
Namely, while the radiation pattern produced by the dipole antenna array is controlled by amplitude and phase of signals applied to the feed ports of the driven dipole array, because of the presence of the parasitic dipole elements on the second and third auxiliary substrates, the sidelobes of the antenna""s radiation pattern are substantially reduced in comparison with a dipole array without parasitic elements of the invention.